This invention relates to a apparatus for depositing a layer of material on to a workpiece.
In many manufacturing processes, including the manufacture of semi-conductor devices, sensors and MEMS, there is a need to deposit layers or thin films of materials onto workpieces. In physical vapour deposition there is a source of material within a chamber whereby material is ejected from the source onto the workpiece to form a layer. The source of material may be a sputter target or it may be an evaporated source or some other source of material that forms at least part of a deposited layer. In any of these cases the material tends to be deposited not only on the workpiece but also on other parts of the chamber in which the process has taken place. Traditionally, the solution has been to cover all long term exposed surfaces with removable shields. Workpieces are usually located on a support and providing shielding around and below the support can be particularly awkward, because such shields can be expensive to form and difficult to locate, given that it is desirable that no threaded fasteners should be used within a chamber, because of the danger of creating damaging particles.
Particular problems arise in connection with the support and the workpiece. Two manufacturing situations tend to exist. The first is where the workpiece is smaller than the support and lies within its periphery. In that case extra deposited material can affix the workpiece to the support or can build up on the surface of the support causing incorrect seating of subsequent workpieces. The second situation is where the workpiece overhands the support. In this arrangement it effectively shields the support, but unwanted deposition can occur on both the edge and the back side of the workpiece. (In some situations manufacturers do require deposition on the edge).
The best solution proposed to date to this problem has been to provide a fixed shield which overlies the periphery of the workpiece and the support, but this has a number of disadvantages. First it tends to preclude deposition on the edge of the wafer, when that is desirable, and secondly it makes the loading of workpieces on to the support extremely complex. Essentially the whole support has to be moved away from the shield so as to give sufficient room for the wafer to be lifted from the support and then removed by a transport mechanism. As very frequently the support will have electrical, cooling and mechanical connections, the need to move the support introduces significant expense and complication.
From one aspect the invention consists in apparatus for depositing a layer of material onto a workpiece including a chamber, a source of material, a workpiece support for supporting a workpiece with an exposed surface facing the material source onto which a layer is deposited, means for loading and unloading the workpiece along a transport path and a shield disposed between the support and the material source for limiting the amount of material deposited on or adjacent to the periphery of the support or workpiece characterised in that the shield lies in the transport path and in that the apparatus further comprises a mechanism for moving the shield out of the transport path during loading and unloading.
The apparatus may further comprise a further shield surrounding the support for shielding the back of the periphery of the workpiece and, in some embodiments, the further shield may shield the edge of the workpiece.
It is preferred that, when in its shield position, the first-mentioned shield forms a labyrinth path with the support, the further shield and/or the workpiece. To enhance this labyrinth path the further shield may have a radial extension.
The apparatus may further comprise means for lifting and lowering the workpiece into or from the transport path and these lifting and lowering means may incorporate or be linked to the mechanism for moving the shield so that as the workpiece is lifted off the support, the shield moves out of the transport path. The lifting/lowering means may include a liftable frame carrying a first set of pins for engaging the workpiece and a second set of pins for engaging the shielding. The second set of pins may serve as the support for the first mentioned shield, when it is in its shielding position as well as during movement of the shield.
The further shield may fall away as it extends radially outwardly to allow greater deposition to take place on its surface before the deposition upon it builds up to a level to contact the workpiece backside, or interfere with workpiece transportation.
The chamber may have or define a ledge formation and in that case the first mentioned shield may have a corresponding and cooperating formation whereby, when the first mentioned shield is in its shielding position, the formations form a labyrinth.
The first-mentioned shield will have a shape which is generally dictated by the shape of the periphery of the workpiece e.g. for a generally circular semi-conductor wafer, the first-mentioned shield will be generally annular.
From a further aspect the invention consists in apparatus for depositing a layer including a source of material, a workpiece support, a first shield for shielding the back periphery of a workpiece on the support and a second shield, interposed between the source and the first shield to shield the first shield.
Although the invention has been defined above it is to be understood that it includes any inventive combination of the features set out above or in the following description.